html,
body {
  height: 100%;
  margin: 0;
  padding: 0;
}

#main {
  position: fixed;
  width: 100%;
  height: 100%;
  left: 0;
  top: 0;
}

#app {
  width: 100%;
  height: 100%;
}
.center {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}
